they spoke from texas prisons where they're serving life sentences for murder. they both say they worked for miguel angel trevino. the ruthless violet leader of a drug cartel recently arrested in mexico. >> i know this man. he's not going to tell you to do something if he won't do it, and that's why a lot of people followed him. >> how much control do you think he had of nuevo laredo? >> absolute control. >> reporter: he was 13 years old when two friends brought him to nuevo laredo, just across the border from texas. he said his life was changed forever. in an instant he went from being a 13-year-old to a killer. >> we pulled up, i couldn't believe what i was seeing. people getting tortured, killed, decapitated. it was kind of hard to believe. i knew that day my life had just changed forever. >> reporter: he then says an argument broke out. miguel trevino wanted to know why retta was there. trevino handed him a gun, they stood over a man tied up on the ground. >> what did they tell you to do? >> to kill that person. i have to do it. if i don't do it, i know what